The synthetic organic chemistry described in this section forms a basis for the research projects described by other members of the Program. A fundamental objective is the synthesis of a series of modified DNA nucleosides that will be incorporated site-specifically into oligonucleotides using automated, solid-state methods. The modified deoxynucleosides selected for study fall into two classes. The first group is related to our investigations on oxidative DNA damage. These substances will be used (a) to construct affinity chromatography substrates for the purification and isolation of DNA repair enzymes (MutM and MutY proteins) that deal with oxidative lesions and (b) to study the mechanisms of action of these enzymes (principally MutY) in the repair process. The second group of deoxynucleosides have modifications related to carcinogenic amines and nitro compounds. They are subdivided into two classes: (a) those that relate to C8-dG adducts and (b) those that rise by attack of the ultimate carcinogen on the N2-position of deoxyguanosine. These defined adducts will be used to establish the mutagenic spectrum generated by the original carcinogen. In addition, they should aid in the solution of structural problems associated both with the nucleosides themselves and with oligomeric DNA containing them. For these purposes, 13C and 15N-labeled nucleosides will be synthesized. Research on the use of new protecting groups for DNA synthesis also will be pursued. This should allow otherwise difficult post-synthetic introduction of base-sensitive lesions into DNA. Analytical studies will investigate the formation of new oxidation products, including cross- linked deoxynucleoside dimers whose structure has not been characterized, and will establish accurate, sensitive assays for oxidation products derived from nuclear and mitochondrial DNA.